大事 (daiji) conjugation
important, valuable, serious matter
大事 (だいじ, daiji) is a na-adjective. Na-adjectives behave like nouns. The word itself never changes — you conjugate だ/です after it, and you need な to put it in front of a noun.
Conjugation table
| Form | Plain (casual) | Polite (~です) | When you use it |
|---|---|---|---|
| Dictionary / plain | 大事だ daijida | 大事です daijidesu | The form you look up. Also the casual “is ~”. |
| Negative | 大事じゃない daijijanai | 大事じゃないです daijijanaidesu | “is not ~”. |
| Past | 大事だった daijidatta | 大事でした daijideshita | “was ~”. |
| Past negative | 大事じゃなかった daijijanakatta | 大事じゃなかったです daijijanakattadesu | “was not ~”. |
| Te-form | 大事で daijide | — | Links to the next clause: “~ and …”. |
| Adverb | 大事に daijini | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 大事な〜 daijina〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 大事なら daijinara | — | “if it is ~”. |
| Conditional (~たら) | 大事だったら daijidattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 大事になる daijininaru | 大事になります daijininarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 大事すぎる daijisugiru | 大事すぎます daijisugimasu | “too ~”. |
| Looks ~ (~そう) | 大事そう daijisou | 大事そうです daijisoudesu | “looks / seems ~” from appearance. |
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Why it conjugates this way
Na-adjectives behave like nouns. The word itself never changes — you conjugate だ/です after it, and you need な to put it in front of a noun.
See the full rules in the adjective conjugation guide.